This invention relates to wireless telephone apparatus capable of sending and receiving telephone calls from an automobile or any other vehicle which is capable of moving within a designated service area.
A conventional wireless telephone system, such as shown in FIG. 1, includes wireless telephone apparatus 1 which communicates by radio signals with base station 2. Base station 2 is connected by land lines to telephone exchange 3. This system is capable of connecting telephone calls between two wireless telephones 1 or wireless telephone 1 and ordinary telephone 4. A plurality of frequency channels are used in communicating between wireless telephone 1 and base station 2, at least one of which is allocated to control and the remainder allocated to operations, i.e., telephone conversations. A telephone conversation is established on an available operating channel by initiating communication on the control channel and exchanging control information, and then switching to the operating channel.
FIG. 2 is a block diagram of a conventional wireless telephone apparatus including an acoustic transmission apparatus, hook switch 21 and radio signal control section 19. The acoustic transmission apparatus includes telephone handset 10, microphone 11, speaker 12, first switch 13, second switch 14, voice control circuit 15, sidetone circuit 16, receiving line 17, transmitting line 18, control keys 20 and control section 22.
Telephone handset 10, which is used during normal conversation, receives an audio signal from radio signal control section 19 via receiving line 17, second switch 14 and sidetone circuit 16. An audio signal is transmitted by telephone handset 10 to radio signal control section 19 via sidetone circuit 16, first switch 13 and transmitting line 18. When handsfree conversation is desired, microphone 11 and speaker 12 are used. Microphone 11 transmits an audio signal to radio signal control section 19 via voice control circuit 15, first switch 16 and transmitting line 18. Speaker 12 receives an audio signal from radio signal control section 19 via receiving line 17, second switch 14 and voice control circuit 15. First switch 13 and second switch 14, which may be relay switches or transmitter switches, connect receiving line 17 and transmitting line 18 with sidetone circuit 16 or voice control 15 in accordance with a select signal generated by control section 22.
Voice control circuit 15 automatically controls speaker volume in accordance with the level of the audio signal detected by microphone 11. As the sound increases during a hands-free conversation, the sound emanating from speaker 12 decreases in volume. Sidetone circuit 16 adjusts gain in order to present a sidetone. Control keys 20 include 12 dailing or digit keys, SEND key, END key and CHANGE key. The SEND key is used to initiate a call and the CHANGE key is used to select either a handset conversation or a hands-free conversation. Control section 22 controls the switching operation of first switch 13 and second switch 14 in accordance with the operation of the CHANGE key, and in accordance with control data from radio signal control section 19. Control section 22 also transmits various key data from control key 20 to radio signal control section 19 via a data bus.
Radio signal control section 19 controls communication between the wireless telephone apparatus and a remote base station. This radio signal control section 19 receives audio signals from handset 10 or microphone 11, and modulates the radio frequency signal which is transmitted to base station 2. Radio signal control section 19 also receives incoming modulated radio frequency signals via an antenna and demodulates these signals to generate either a control signal or an audio signal which is sent over receiving line 17.
When a telephone call is initiated with this wireless telephone apparatus, the user first operates the 12 dialing or digit keys of control keys 20 and then operates the SEND key. The call origination signal and the dialing signal originated by the wireless telephone apparatus are transmitted by radio signal control section 19 to base station 2 over a control channel and, according to a command signal transmitted from base station 2, radio signal control section 19 enables the wireless telephone apparatus to transmit over an available operating channel. Thereafter, a telephone conversation is established between the wireless telephone apparatus and a remote telephone via base station 2.
In the conventional wireless telephone apparatus, the telephone conversation can take place over handset 10 or speaker phone 10-11, depending on the operation of the CHANGE key. If first switch 13 and second switch 14 connect receiving line 17 and transmitting line 18 with sidetone circuit 16 in accordance with the operation of the CHANGE key, then handset 10 is used. If first switch 13 and second switch 14 connect receiving line 17 and transmitting line 18 with voice control circuit 15 in accordance with the operation of the CHANGE key, then microphone 11 and speaker 12 are used.
If the wireless telephone apparatus is called by another telephone, base station 2 transmits a call receipt signal, together with the appropriate available operating frequency channel, over a control channel. Upon receipt of the call receipt signal and information concerning the available operating channel, radio signal control section 19 enables the wireless telephone apparatus to communicate over the assigned operating channel. Moreover, in the state of standby, first switch 13 and second switch 14 connect receiving line 17 and transmitting line 18 with voice control circuit 15 in accordance with a control signal from control section 22. Control section 22 generates the control signal in accordance with control data received from radio signal control section 19 via the data bus. Then, if the wireless telephone apparatus is called by another telephone when it is in the standby condition, radio signal control section 19 generates an alert signal. This alert signal is generated until the user of this wireless telephone apparatus operates either the SEND key or hook switch 21, or until radio signal control section 19 receives a clearing signal from base station 2. The alert signal is transmitted by radio signal control section 19 to speaker 12 via receiving line 17, second switch 14 and voice control circuit 15 to ring speaker 12.
The above described wireless telephone apparatus has a number of disadvantages. In the hands-free conversation mode, when a microphone and speaker are used, an expensive and complicated voice control circuit, which includes an automatic speaker volume control device responsive to the level of the audio signal detected by the microphone, is required. Also, in the hands-free conversation mode, the user cannot engage in a private conversation because a microphone must be used. Furthermore, as ambient sound increases during the hands-free conversation mode, the sound from the speaker decreases in volume so that the telephone conversation is difficult to hear.